1. Field of the Invention
This invention relates to a multi-input amplitude and phase measuring device which measures the phase differences and the amplitudes of signals of the same frequency received by means of a plurality of antennae.
2. Description of the Related Art
A multi-input amplitude and phase measuring device measures the phase differences and amplitudes of signals received by means of a plurality of measurement antennae arranged in a juxtaposed relationship to each other to find the direction of arrival of a radio wave or to identify an unwanted radiation source such as an electronic circuit.
To this end, using a signal received by one of the plurality of antennae as a reference signal, the phases and the amplitudes of measurement signals received by the other antennae are measured.
A construction and operation of a conventional multi-input amplitude and phase measuring device will be described with reference to FIG. 1.
The conventional multi-input amplitude and phase measuring device includes an antenna 1, a local signal generator 3, a mixer 2, a band-pass filter 7, an antennae 4, 14, 15 and 16, a switch 17, a local signal generator 6, a mixer 5, a band-pass filter 8, an analog mixer 9, a band-pass filter 10, a vector detector 11, an arithmetic unit 12 and display unit 13.
Antenna 1 receivers a reference signal of frequency f.sub.RF. Local signal generator 3 generates a local signal of frequency f.sub.LO. Mixer 2 multiplies the reference signal received by antenna 1 and the local signal of frequency f.sub.LO together to output the resultant signal. Band-pass filter 7 passes only a signal of frequency f.sub.RF -f.sub.LO of the signal supplied from mixer 2. Antennae 4, 14, 15 and 16 receive measurement signals of frequency f.sub.RF.
Switch 17 selects one of antennae 4, 14, 15 and 16. Local signal generator 6 outputs a local signal of frequency f.sub.LO +.DELTA.f. Mixer 5 multiplies the measurement signal received by the antenna selected by switch 17 and the local signal of frequency f.sub.LO +.DELTA.f and outputs the resultant signal. Band-pass filter 8 passes therethrough and outputs only the signal of frequency f.sub.RF -f.sub.LO -.DELTA.f of the signal supplied from mixer 5.
Analog mixer 9 multiplies the signal supplied from band-pass filter 7 and the signal supplied from band-pass filter 8 together to output the resultant signal. Band-pass filter 10 passes only a signal of frequency .DELTA.f of the signal supplied from analog mixer 9. Vector detector 11 detects the phase difference between the measurement signal and the reference signal and the amplitude of the measurement signal using the signal of frequency .DELTA.f supplied from band-pass filter 10. Arithmetic unit 12 performs a process for displaying the data of the phase and the amplitude detected by vector detector 11. Display unit 13 displays the data processed by arithmetic unit 12.
Operation of the conventional multi-input amplitude and phase measuring device will be described below with reference to FIG. 1.
A reference signal of frequency f.sub.RF received by antenna 1 is multiplied by a local signal of frequency f.sub.LO supplied from local signal generator 3 by mixer 2. Then, only the signal of frequency .vertline.f.sub.RF -f.sub.LO .vertline. passes through band-pass filter 7 to be outputted as an IF (intermediate frequency) signal.
Meanwhile, the measurement signal of frequency f.sub.RF received by antenna 4 is delivered through switch 17 to mixer 5, by means of which it is multiplied by local signal 6 of frequency f.sub.LO +.DELTA.f supplied from local signal generator 6 by mixer 5. Then, only the signal of frequency .vertline.f.sub.RF -f.sub.LO -.DELTA.f.vertline. passes through band-pass filter 8 and is outputted as an IF signal.
The output signals of band-pass filters 7 and 8 are then multiplied by analog mixer 9, and only the signal of frequency .DELTA.f passes through band-pass filter 10 and is outputted. If the signals supplied from band-pass filters 7 and 8 have the same spectra, then the signal supplied from band-pass filter 10 is a single frequency signal which includes phase information of the measurement signal of antenna 4 in a case where the signal received by antenna 1 is used as a reference for the phase, and the amplitude and the phase of the signal can be measured by vector detector 11.
Further, if antennae 14, 15 and 16 having the same characteristics as antenna 4 are individually disposed at required measurement points and switch 17 is switched suitably, then the amplitudes and the phases of the signals detected at the plurality of measurement points can be measured without scanning a measurement antenna. The time required for measurement, which normally takes ten minutes or more when measurement is performed at a plurality of measurement points using a single measurement antenna, can be reduced by disposing a plurality of measurement antennae in a juxtaposed relationship to each other.
Then, the results of measurement of amplitude and phase are processed suitably at arithmetic unit 12, and the results of the processing are displayed on display unit 13.
With the conventional multi-input amplitude and phase measuring device, a mechanical switch is usually employed as switch 17. However, since a mechanical switch requires several tens of ms for switching, the more the number of measurement antennae or the number of switching contacts of the switch is, the larger the measurement time is. The mechanical switch has additional problems difficult to solve such as the problem of the life of the switch arising from repetitions of high speed switching and the variation of the insertion loss.
Where a semiconductor switch is used as switch 17, although the problem of the switching time is solved, it is difficult, at the present time, to achieve sufficient isolation compared with a mechanical switch.
Further, with a method using a switch, in a case the measurement signal is one pulse signal, all switching and measurement are not completed until a next pulse is generated. Therefore, it takes a longer time to measure, using a pulse with a long cycle period.